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Discussion Starter · #1 · (Edited)
I have started to collect parts for a future engine build and thanks to the mother of all Black friday deals, I picked up a set of Manley 300M rods with ARP 625+ bolts. Essentially, I
voted with my pocket book when it came to deciding what the strongest Mod motor connecting rod was.

Here is what John Mihovetz had to say about the Manley 300M I beam rods:

"The Manley rod is a serious piece. The original I beam rods lasted reliably up until around 1300 hp. Thus the 300 M rods were designed. There are many other options,
Oliver probably being the best, the problem is the wait time. As far as weight is concerned, heavy seems to keep getting mentioned. Just what does that mean and being relative to what?
The 4.6 300 M rods are around 650 grams give or take a few. If you look at a comparable Oliver or any other manufacturers rods they simply are heavier. The normal Manley I beam rod is
600 grams. We have reliably made over 1700 hp with the Manley rod and to date have never, ever bent one, broke one , or damaged one. We ran over the weekend in
Las Vegas testing with the Pro Stock guys for Pomona. 10 passes between 6.79 and 6.73. Best pass was 6.731 @210.96 The best Pro Stock that
I saw was Greg Anderson @ 6.82 @ 203.5 10 passes, 10.7 to 1 compression, 40 psi boost and 9200 rpm shifts, I'd call the Manley rod a good piece for the money.
John Mihovetz"


IMG_8185.jpg IMG_8186.jpg IMG_E8180.jpg

One note about the weight of the 300M rods: Manley says that these rods weigh 695 grams. as a comparison, the factory 2001 Cobra rod weighs 575 grams.
No doubt I'll be going with heavier than stock pistons as well so the machine shop will need to re balance the factory crank.
 

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Discussion Starter · #2 ·
The critical factors that determine the limits of a connecting rod and the rod bolt itself are: engine speed, RPM,stroke and piston weight. Here ARP shows why excessive engine speeds can kill a sub standard rod as loads triple, not double as engine speed goes up:

"The first step in the process of designing a connecting rod bolt is to determine the load that it must carry. This is accomplished by calculating the dynamic force caused by the oscillating piston and connecting rod. This force is determined from the classical concept that force equals mass times acceleration. The mass includes the mass of the piston plus a portion of the mass of the rod. This mass undergoes oscillating motion as the crankshaft rotates. The resulting acceleration, which is at its maximum value when the piston is at top dead center and bottom dead center, is proportional to the stroke and the square of the engine speed. The oscillating force is sometimes called the reciprocating weight. Its numerical value is proportional to:

It is seen that the design load, the reciprocating weight, depends on the square of the RPM speed. This means that if the speed is doubled, for example, the design load is increased by a factor of 4. This relationship is shown graphically below for one particular rod and piston."


A while back, there was a lengthy thread https://www.modularfords.com/threads/245777-Cobra-Manley-H-Beam-Snapped-in-Half on a Manley H beam rod failure and I suggested that the failure was due to excessive RPMS and that the Manley H beam rod was operating outside its intended design power application. As you can see from the ARP chart, the loads that a connecting rod must endure increase dramatically as RPM's go up and thats not taking into account power adders such as a supercharger, turbo or nitrous.

To quote Manley:

"A WORD ABOUT HORSEPOWER RATINGS...

You will see that we list "horsepower ratings" for each different series/application of Manley connecting rods. However, it is very important to understand that these "ratings" are somewhat subjective. The critical factors that significantly influence the fatigue life of connecting rods (and the horsepower rating) are RPM, stroke, piston weight and power adders. In certain cases, our horsepower ratings may be conservative. Call our tech line if you are unsure based on your specific application."

In choosing the Manley 300M rod with the ARP 625 plus bolts, I'm getting the strongest solution possible and I don't want to worry about a bending or otherwise breaking a rod or damaging a rod bolt since those are the most highly stressed parts in an engine.
 

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Jan,

The tensile loading on the rod bolts does not triple as you state. The tensile loading actually goes up as the square of the relative increase in rpm. If you double the rpm, the relative increase is a factor of 2x. That means the tensile loading increases by a factor of 4 not three. If you triple the rpm, the relative increase is a factor of 3x. That means the tensile loading increases by a factor of 9!

In fact the clips you have posted from the ARP catalog specifically state this. While I know you are enthusiastic about the new rods you have purchased please try to be factual about these sorts of phenomena. We do not want to promulgate misinformation for follow on readers.


Ed
 

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Does anyone have any thoughts on the 300M rods compared to the Weisco Boostline rods? 300M has a weight of 695g, with the Weiscos coming in at 696g from what I can find, so a negligible difference. Both are touted at being capable of 2000hp+, but the 300M rods have a premium price point.
 

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Does anyone have any thoughts on the 300M rods compared to the Weisco Boostline rods? 300M has a weight of 695g, with the Weiscos coming in at 696g from what I can find, so a negligible difference. Both are touted at being capable of 2000hp+, but the 300M rods have a premium price point.
I have held both in my hands and used both in engines, Robert. I think they are very comparable from a strength point of view. I like the Wiesco sculpting of the rod beam in the area immediately above the big end of the rod. This is a design cue from some high end F-1 connecting rod suppliers. The technique spreads the combustion loading more evenly across the top rod bearing. The F-1 rod purveyors and users were quite complimentary about the design and the improvement in upper rod bearing life.

While we are not F-1 competitors, the design benefits still accrue to our engines if we choose to use the Boostline Rods. I think the biggest argument that translates into real world differences is the pricing. You basically get the same rod at half the price with a better treatment of the upper rod bearing.

This is a picture of a Teksid race block that literally blew the main webs and the crank out of the block.
175611

The engine was using Boostline rods and Gibtec pistons, both the rods and the pistons survived and lived to fight another day. The rods were inspected for straightness, length, and bore concentricity at the pin and crank pin ends. They were unchanged from their out of the box dimensions. There were no scratches or gouges on them and only a few shiny spots where they were abraded by what looked like block casting.

Here is a pic of the rods and pistons immediately after they came out of the engine;
175612

Other than inspection and replacing the rod bearings, the rods (and pistons) were reusable and were in fact reused in the replacement engine.

The Wiesco Boostline rod is a very high quality rod on par with the best stuff you can buy today. I believe if you choose the Boostline rods for your build, you will be very pleased with your decision and it will give you about $1K to spend elsewhere in the engine.

Ed
 

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Discussion Starter · #6 ·
Jan,

The tensile loading on the rod bolts does not triple as you state. The tensile loading actually goes up as the square of the relative increase in rpm. If you double the rpm, the relative increase is a factor of 2x. That means the tensile loading increases by a factor of 4 not three. If you triple the rpm, the relative increase is a factor of 3x. That means the tensile loading increases by a factor of 9!

In fact the clips you have posted from the ARP catalog specifically state this. While I know you are enthusiastic about the new rods you have purchased please try to be factual about these sorts of phenomena. We do not want to promulgate misinformation for follow on readers.

Ed
in my example, I was discussing reciprocating weight, not tensile loads. Yes, reciprocating weight increase with the square of rpm, being 4 times as great at 1,800 rpm as at 900 rpm and 64 times as great at 7,200 rpm.
 

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Discussion Starter · #7 ·
Does anyone have any thoughts on the 300M rods compared to the Weisco Boostline rods? 300M has a weight of 695g, with the Weiscos coming in at 696g from what I can find, so a negligible difference. Both are touted at being capable of 2000hp+, but the 300M rods have a premium price point.
The Manley I beam rod uses 300M steel billet while the Weisco rod uses 4340 forged steel. Furthermore, the Manley 300M I beam rod is made in USA while the Weisco Boostline rod is "finished in USA."

The Manley rod costs more than the Weisco due to the use of the more costly material, manufacturing method and the fact that it is made in USA rather than "finished in USA." For sure the Manley 300M I beam rod is the stronger part based on material use alone. The big question is: do you need the unquestioned strength of the Manley 300M I beam rod or will your application reliably preform with a less expensive rod?
 

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The Manley I beam rod uses 300M steel billet while the Weisco rod uses 4340 forged steel. Furthermore, the Manley 300M I beam rod is made in USA while the Weisco Boostline rod is "finished in USA."

The Manley rod costs more than the Weisco due to the use of the more costly material, manufacturing method and the fact that it is made in USA rather than "finished in USA." For sure the Manley 300M I beam rod is the stronger part based on material use alone. The big question is: do you need the unquestioned strength of the Manley 300M I beam rod or will your application reliably preform with a less expensive rod?
Some time ago a service tech in my local stereo repair shop was diligently trying to dissuade me from spending money on a system and speaker set that he maintained would not be any different than a much less expensive system. The essence of his argument was that while the more expensive system had a measurably wider dynamic range than the lower priced system, the simple fact of the matter was it required instrumentation to measure or evaluate the frequency response at the extremes. Even more significantly, and really to the point, my ears could not hear sounds in those frequency ranges so why was I spending the money for an audio system my ears could not distinguish from a less costly but still very nice system.

We can easily get caught up in the automotive performance parts equivalent of this type of subterfuge. Even worse, it is usually expanded upon and propagated by well-meaning but uninformed enthusiasts that really believe that the hyperbole they use to promote their favorite component is both true and relevant.

Let us take a moment and evaluate the 4340 vs 300M arguments;

4340 and 300M are essentially kissing cousins - both metallurgically and from a physical properties perspective. The primary difference in their composition comes down to slight differences the percentages of a few select elements;

..........................................300M..................4340
  • Carbon ........... 0.40 - 0.46% ..... 0.37 - 0.44%
  • Manganese .... 0.65 - 0.90% ..... 0.55 - 0.90%
  • Silicon ........... 1.45 - 1.80% ...... 0.15 - 0.35%
  • Chromium ..... 0.79 - 0.90% ...... 0.65 - 0.95%
  • Nickel .............1.65 - 2.00% ...... 1.55 - 2.00%
  • Molybdenum . 0.30 - 0.45% ...... 0.20 - 0.30%
  • Vanadium ...... 0.05 - min ........ not applicable

The physical properties of the two alloys are also quite revealing;

........................................300M.................4340
  • Tensile Str ........ 340 ksi ............. 287 ksi
  • Yield Str ........... 260 ksi ............. 190 ksi
  • % Elongation .... 6 - 9.5% ........ ..11 - 23%
  • % Reduction .... 10 - 34% ...........39 - 63%
With the exception of the differences in tensile strength there are many who maintain that 300M was largely a marketing ploy to sell a new formulation at a preferred price point higher than 4340. Without the ability to read minds there is likely no way to ever know the truth about that particular assertion.

Not withstanding the inability to read minds, the chemical properties suggest two very similar steels and the actual physical properties reinforce that conclusion. In actual fact, the physical properties suggest that the 4340 steel could be a tougher, less brittle steel than the 300M steel, making it more suitable for use in connecting rods. Certainly, a more cost effective steel.

Jan represents the Manley offering as, "The Manley I beam rod uses 300M steel billet while the Wiseco rod uses 4340 forged steel."

Manley's position on their rods is that they are forged from 4340 or 300M, see Manley catalog clip below.
175614

Manley states in their catalog the rods can be had in either4340 or 300M material. My sources advise me that the actual rod forging has been made in China and finished machined either by or for Manley in the US. Additionally, the lighter weight rod that Manley refers to as their 675g standard weight rod is actually the 4340 steel rod. The heavier weight rod that Manley refers to as their 690g Pro Series rod could be either 4340 or 300M steel as their catalog page indicates, although I would expect it would be 300M.

When we look critically at the two rods and their materials it becomes clear that the primary benefit of the Pro series rod is the additional 15g of steel that was added to the finished Pro series rod. The distinction between the 4340 and 300M materials is distinction without a difference, for this application.

In addition to connecting rods being able to withstand the power being directed to them by the piston for transfer to the crank they also provide a blow off valve, so to speak, for unintended whoops's while operating the engine at or near its peak power levels. They additionally represent a frontline defense for the improbable and unthinkable things that can only happen to a performance engine that belongs to you!

The pic below the next paragraph is a pic of a Manley H-Beam that was in a cylinder with a faulty injector. The injector leaked fuel into the intake port (and later at startup, the cylinder), bending the rod on the first full cycle of the engine at start up, by hydraulicing that one hole. Other than a quick initial sharp sound there was for all intents and purposes no other audible red flags. The car ran a very low nine second pass immediately afterwards.

After showing low leakage but also low compression in that one cylinder, the engine was torn down for inspection the following weekend, and this is what was found inside;
175613

This rod did everything you could possibly ask a rod to do. It softened the blow of hydraulicing that cylinder, it bent instead of breaking, it did not act like a Weed Wacker inside the crankcase with an iron cord and heavy weight at the end, swinging around and destroying everything in sight. It also did not flush fine cast iron or steel particulate matter throughout the engine and oiling system destroying other untold numbers of parts and dollars.

Now think about all the hyperbole we have been subjected to about how unsuitable the Manley H-Beam rods are for a high horsepower version of our engines. How many times have you actually seen, not heard of but actually seen (in person or photographically) a Manley H-Beam that exhibited an ultimate strength failure resulting in two pieces of connecting rod? For me the answer is zero! I would bet it is for you too.

Soooo, just like that perfect audio system I wanted to buy that the tech support guy finally talked me out of, why buy something for a failure you have not, know no one who has and probably never will personally experience?

If you are intent on spending the monies, and I understand fear of the unknown, buy the Boostline rods and put the other $1K to work elsewhere in your hot rod.

Ed
 

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Now think about all the hyperbole we have been subjected to about how unsuitable the Manley H-Beam rods are for a high horsepower version of our engines. How many times have you actually seen, not heard of but actually seen (in person or photographically) a Manley H-Beam that exhibited an ultimate strength failure resulting in two pieces of connecting rod? For me the answer is zero! I would bet it is for you too.
Ed
Ed, you must have forgotten about the one I broke in half a few years ago. Here is a couple refresher pics.


 

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You are absolutely right, Tony! I forgot and that is unquestionably a tensile strength failure where the rod appears to have been pulled apart in the beam. I take back all my H-beam broken rod commentary. Just for grins, if there are any other guys out there with failed versions of this rod please add your commentary and observations you may have about the version of the failure you experienced.

Particularily in consideration of the obvious failure Tony (and potentially others have experienced) I understand and agree with the ounce of protection and the pounds of safety ethic. With that in mind I would also add the Wiesico Boostline alternative to that same bucket of better rod choices. I believe all them would perform very well although the heavier Manley I-Beam and the Wiseco Boostline alternatives would most likely provide the most robust choices.

An engine builder's selection, in the end, would be a composite decision (aren't they all?) predicated on perceived strength and available budget. In the FWIW bucket I while I was digging around on the Manley site, I ran across a new connecting rod offering from them. They call it their H-TUFF series rod they position it between their traditional H-Beam offerings and their I beam offerings. This is what the rod looks like from the Manley catalog;
H-TUFF Manley.png
As Manley indicates in their last bullet point in their catalog, the H-TUFF design uses a wider beam and increased cross section along with a pin surround design that takes the rod bean contour entirely around the top of the wrist pin area. Summit prices the rods (MAN-15042R-8) at $867.99, which would position them as the next step up both price and strength -wise from their traditional H-Beam offerings.

Ultimate strength tensile failures in the beam section of a rod are normally associated with high engine speeds, 8500 rpm and higher. Connecting rod beam loading in a crank slider mechanism (our rotating assemblies) is comprised of both a compressive and a tensile loading. Although the connecting rod's compressive loading of the beam from combustion pressures does not rise with rpm (in fact it decreases) the tensile loading goes up as the square of the increase in engine rpm, i.e double the engine rpm (increase is a factor of 2x) and you will have four times the tensile loading. Tripple the the engine rpm (increase is a factor of 3x) and you will have nine times the tensile loading.

The rod tensile loading occurs at TDC overlap rather than TDC firing. At TDC firing you have both the compressive forces required by the engine's compression ratio and boost level the engine operates at along with the rapidly expanding volume of fuel and air that was ignited 20 degrees or so before TDC firing and is expanding as the piston is rising towards TDC.

At TDC overlap you have no compression or expanding burning fuel moisture to soften the load the connecting rod sees as the piston approaches TDC overlap and the rod has to change piston direction to keep it from going through the cylinder head. In this undamped, unrestrained environment the rod beam (and the rod bolts) will see the maximum tensile loading they will experience throughout the engine's four cycles of operation. It is at this point that connecting rod, connecting rod fastener and wrist pin failures occur.

Beam failures of the type Tony experienced can only be avoided by increasing rod beam cross sectional area, decreasing reciprocating mass or reducing peak engine rpm. Both of the Manley I_Beam offerings, their new H-TUFF rod line and the the Wieseco Boostline rods all provide increased beam cross section which will allow higher engine speeds, all reciprocating weights being equal. The choice for the engine builder is how high an rpm do you intend to run the engine and how much financial stress from the purchase of the rods can your build budget tolerate.

If you live in the below 8500 rpm world (as most of us do) and your pistons weigh less than bowling balls, you can be quite safe with a typical H-Beam design. When rod failures do occur they are usually not compressive but rather due to an ultimate strength failure where the rod is literally stretched apart by the tensile forces acting on it at TDC overlap. Thise forces are almost always associated with heavy rotating assemblies operating at speeds in excess of 8500 rpm.

All rational thinking aside, I also understand the fear factor of a massive engine failure attributable to a connecting rod failure. There is a value to peace of mind. If even a remote potential for engine failure, attributable to a failed rod beam, is eating away at your peace of mind then, that is the best reason to go as far up the connecting rod purchase ladder as your build budget allows.

Ed
 

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FWIW, I run Manley standard weight I beams (14518) in my primary engine and they have delivered excellent performance to date. I did pick up a set of Molnar power adder rods for the my 2nd engine that I've been acquiring parts for.
 

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Discussion Starter · #12 ·
With the exception of the differences in tensile strength there are many who maintain that 300M was a marketing ploy to sell a new formulation at a preferred price point higher than 4340. Without the ability to read minds there is likely no way to ever know the truth about that particular assertion.

Notwithstanding the inability to read minds, the chemical properties suggest two very similar steels and the actual physical properties reinforce that conclusion. In actual fact, the physical properties suggest that the 4340 steel would be a tougher, less brittle steel than the 300M steel, making it more suitable for use in connecting rods. Certainly, a more cost effective steel.
https://www.houghtonintl.com/sites/default/files/resources/article_-_heat_treatment_of_landing_gear.pdf

As the above article by an Phd Engineer and SAE member shows , 300M is a vacuum melted low alloy steel with the inclusion of vanadium and a higher silicon composition. It has a very good fatigue strength and resilience. Where fracture toughness and impact strength are crucial, 300M is a great choice. Furthermore, common applications of 300M steel include Aircraft Landing Gear Airframe Parts Missile Components Motorsport Applications. 300M steel is no marketing gimmick as some might suggest. The 300M alloy is supplied by the Timken Co of Canton, Ohio and that is one reason why the Manley 300m I beam rod commands a higher price than the Boosline rod.



More testimony on the Manley 300M rod from Accufab racing's Fred Grochuliski: " it's so tough that it tears up production tooling, but its proven bulletproof." By the way, I value what Accufab says in regards to mod motor parts selection as to my knowledge, no one else has pushed the limits of that platform further than anyone else.

5.88 seconds at nearly 255 mph using the Manley 300M I beam rods in a 4.6 Ford Mod Motor
 

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I don't believe anyone is arguing the manufacturing and heat treatment processes for 300M, Jan — although the article is interesting. The argument is that 300M was by and large a marketing ploy by Timken. As the article points out early on the 300M steel is essentially a 4340 steel that was modified by increasing the amount of silicon, vanadium, carbon and molybdenum content compared to 4340. The actual physical properties of the two steels so closely approximate one another that, unless you have a specific need for increased tensile strength, there is no practical difference.

The actual tensile strength range of the 300M, from your link, is 269 to 305 ksi while 4340 in a commonly used heat treatment is 287 psi. Using the numbers from your linked article makes the differences between the two steels even less significant than I had originally indicated. To be fair there are specialized applications where 300M's unique physical properties can be advantageous. Connecting rods do not appear to be one of those applications. From the numbers 4340 outperforms 300M in both the % elongation and % reduction categories and while both metals are tough, the 4340 appears, from the physical properties, to be less brittle or if you will likely to crack. Again we are splitting hairs here because either steel is very difficult to crack.

I don't think anyone has critically reviewed your rods as inferior, Jan. If you like them that is excellent and it is all that is required for your purchase to be right for you. That however does not mean it is necessarily the best pick for everyone else. Your rods came to you at a fire sale price. It is significant that you did not previously buy them at full retail price. The obvious implication is that you either did not think they warranted the price or your budget did not provide for that type of component purchase — which goes to my perfect stereo story.

I think it is great that you found a deal on a nice set of rods. That does not necessarily mean that the same set of rods, at their normal retail price point, would be a good choice for everyone else. In fact when you could have bought them at full retail, you chose not to. That speaks volumes to your unspoken but very real value assessment of the product.

Enjoy your rods, be happy and don't get your panties all wadded up over perceived but non-existent attacks on your product choices or purchasing practices. And while we are at it, please try to be factual and drop the hyperbole. It benefits no one and serves to potentially misinform people who subsequently read these threads actually trying to learn and understand some of these product distinctions.


Ed
 

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FWIW, I run Manley standard weight I beams (14518) in my primary engine and they have delivered excellent performance to date. I did pick up a set of Molnar power adder rods for the my 2nd engine that I've been acquiring parts for.
Even the standard weight I-Beam is a step up in cross section and strength, Tony and FWIW I like them too. Of course that and $5 will get you a coffee at Starbucks. :)

Tom Molnar makes some very impressive parts. He was the or one of the founders for K-1 Technologies, that I believe Wiseco bought. Tom's pieces are very well thought out and very high quality - I like his stuff a lot.

Ed
 

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Thanks everyone for the information. I personally find it very hard to not pick a part based on price. It's very easy for me to get caught up in the sometimes incorrect belief of "oh this part option cost 2x as much, it must be 2x better". Have to love our minds. I'll be going with the boostline rods. Beautiful pieces!

Sent from my SM-G975U using Tapatalk
 

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Your point about the difficulty in removing pricing from the parts selection process is well made, Robert. Modular engine builders are fortunate to have a relatively wide range of very good component selections in the connecting rod category. With a rich field of superior product selections, the most important consideration becomes what you want and feel good about using. After that, the remainder of any discussion is simply rhetorical noise and artifact. My prediction is that you will be very happy with your selection.



Ed
 

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Discussion Starter · #17 ·
I don't think anyone has critically reviewed your rods as inferior, Jan. If you like them that is excellent and it is all that is required for your purchase to be right for you. That however does not mean it is necessarily the best pick for everyone else. Your rods came to you at a fire sale price. It is significant that you did not previously buy them at full retail price. The obvious implication is that you either did not think they warranted the price or your budget did not provide for that type of component purchase - which goes to my perfect stereo story.

I think it is great that you found a deal on a nice set of rods. That does not necessarily mean that the same set of rods, at their normal retail price point, would be a good choice for everyone else. In fact when you could have bought them at full retail, you chose not to. That speaks volumes to your unspoken but very real value assessment of the product.

Ed
I'll agree with you that one perfect rod that covers every situation simply does not exist. For example, In the Australian Super car series, the majority of the teams use a Carrillo H beam rod that is lighter than the Manley 300M I beam rod I will be using in my engine. However, the engine builder that supplies the majority of the supercar filed will milage out those Carrillo rods at 5K intervals thus trading longevity for lower reciprocating weight and faster engine response and this approach does not cause problems because the rods are regularly replaced. In My case, I can't afford to "milage out" major engine components like rods so from the beginning, my plan was to use the strongest rod possible and thus not worry about an engine failure later on. Now, I will say that in terms of the strongest "put it in there and forget about it" 4.6 Ford mod motor rod without having to worry about the price(or too crazy to care) is the Manley 300M I beam.

Of corse cost is a consideration for most people and if that's case, then a Manley 4340 I beam rod or the Turbo Tuff H beams paired with the ARP 2000 bolts would be a better choice. I'm not immune to cost considerations either and while it would be nice to use a Bryant billet crank, the factory forged unit will work fine, so I'll spend my money elsewhere.

As for not buying the 300M I beam rods with the ARP 625+ bolt optional the full retail price, I thought that the Manley 300M I beam rods were worth the cost and I decided a while back that I would be using that rod no matter what. But , I also knew that by the end of the year, the warehouse where I buy most of my go fast Mustang hardware from would offer some really good deals and they did so I bought a set.
 

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All good rational reasons and reasoning, Jan. The most important litmus test though is, are you happy with the product and decision. To the extent I can assess that, I would have to say you are, so — that makes the product and purchase as right as is possible for you. I am certain (as I know you are also) that those rods will perform up to your expectations and then some.


Ed
 

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This thread about the rods has been very interesting. But what is SCARY is that motor with the blown out bottom end! It looks like both rod alloys are strong enough and the weak link is the block. I wish I knew more about it. What caused the failure, what HP, what oil pressure, what RPM, oh so many questions?

Since piston speed is a function of stroke and rpm I don't think you can generalize a safe RPM limit since shorter strokes vs longer strokes generate less stress.
 

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This thread about the rods has been very interesting. But what is SCARY is that motor with the blown out bottom end! It looks like both rod alloys are strong enough and the weak link is the block. I wish I knew more about it. What caused the failure, what HP, what oil pressure, what RPM, oh so many questions?
That engine was a maximum effort race engine running methanol, very high compression, max effort race cams and 30 psi (or thereabouts) of boost along with an aggressive tune. There was also a contributory whoops. What you are looking at is an ultimate strength failure in a major engine component, in this instance, the block. It is improbable, but not impossible, that you would experience a similar failure. One of severa, both significant and important, events was the way the rods handled the failure, their condition and their reusability.

Since piston speed is a function of stroke and rpm I don't think you can generalize a safe RPM limit since shorter strokes vs longer strokes generate less stress.
If you ask ARP to evaluate your rod bolt choices they will inquire about everything you have already identified and a few more variables prior to providing their opinion. As a general rule of thumb if your maximum engine speed is at 8500 rpm or below, you use fairly typical pistons with a quality rod selection then an ARP 2000 bolt will perform admirably in your engine. If your maximum engine speed is above 8500 rpm you ought to be looking at 7/16" fasteners made from ARP 2000 steel.

If your budget will allow the stress, ARP offers Custom Age 625+ steel rod bolts through normal distribution channels like Jegs and Summit but the fasteners come at elevated prices meaning between $500 to $570 for a set, depending on whether they are ⅜ or 7/16 and whose rods they are for. That said, the 625+ bolts are as much better than the 2000 bolts than the 2000 bolts are better than the 8740 bolts.

Buy adequacy don't buy overkill.

Ed
 
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